Plant scientists have recognized for many years that the hybridization of closely related plants may result in the production of offspring having a combination of desirable traits which previously were possessed separately by the parent plants. Also hybrid plants of various crops commonly have possessed a vigor or heterosis which has contributed significantly to the crop yield and accordingly has been of considerable economic importance.
Since the plants selected for hybridization studies commonly are capable of undergoing both self-pollination and cross-pollination, the desired crossing often has been difficult to achieve on a reliable basis while operating on a commercially viable scale. Accordingly, controlled cross-pollination must be achieved in the substantial absence of self-pollination. A common technique heretofore utilized to accomplish this goal has been the use of cytoplasmic male sterile plants as the seed parent which are grown as a substantially uniform population adjacent another substantially uniform population of plants from which the pollen is derived. Such technique has required precise control of the planting patterns, sufficient pollen transfer from one block of plants to another, and precise control of the seed harvest to preclude comingling of the two different seed products which are produced.
In U.S. Pat. No. 3,842,538 is disclosed a method of hybrid seed grain production wherein the bulk planting of cytoplasmic male sterile parent and the pollen parent is proposed. The seeds capable of forming hybrid plants are thereafter separated from the non-hybrid seeds on the basis of color. Such seed separation technique still would be tedious; however, and is not believed to have been commercially adopted. See also, articles by D. E. Falk, K. J. Kasha, and E. Reinbergs appearing in Proceedings of the Fourth International Barley Genetics Symposium, Edinburgh, July 22 to 29, 1981 (Edinburgh University Press) pages 778 to 785, and by D. E. Falk and K. J. Kasha appearing in Crop Science, Vol. 22, March-April, 1982, page 450, where a tight linkage between genetic male sterility and a shrunken endosperm is discussed.
While considerable success has been realized in the past through the adoption of various well-known hybridization techniques, the need nevertheless has remained for alternate less tedious, more efficient, or otherwise improved hybridization routes. Additionally, for many crops commercially feasible hybridization technology is yet to be implemented in spite of continuing research by dedicated plant scientists working around the world.
An example of a crop which is yet to benefit from the commercial availability of seed capable of growing hybrid plants is rape (i.e., Brassica napus or Brassica campestris). While not necessarily recognized by the general public, rape (and particularly high quality forms thereof known as canola) is being grown as an increasingly important oilseed crop and a source of rapeseed meal in many parts of the world. The oil may serve as a high quality vegetable oil and the meal may be used as a nutritious protein concentrate for livestock. The importance of rape as an agronomic crop is discussed in (1) Highlights of Agricultural Research in Ontario, December 1982, at Pages 18-19 in an article by W. D. Beversdorf and David J. Hume entitled "Canola: A New Oilseed Crop for Ontario", and in (2) the Ontario Ministry of Agriculture and Food Factsheet No. 82-017, February 1982, entitled "Spring Canola in Ontario" by D. J. Hume, R. J. McLaughlin and W. D. Beversdorf.
Representative publications of researchers working in the area of rapeseed technology who have identified cytoplasmic male sterility in rape plants are identified below:
Bannerot, H., Boulidard, I., Cauderon, Y., and Tempe, J. (1974). "Cytoplasmic Male Sterility Transfer From Raphanus to Brassica." Proc. Eucarpia Meeting Cruciferae Vegetable Crop., Sect. 25:52-54. PA0 Bartkowiak-Broda, I., Rousselle, P., and Renard, M. (1979). "Investigation of Two Kinds of Cytoplasmic Male Sterility in Rape (Brassica napus L.)". Genet. Polon. 20:487-497. PA0 Ohkawa, Y., Shiga, T., and Ishige, T. (1979). "Male Sterility-Inducing-Cytoplasm in Brassica campestris var. rapifera", Annual Report, Division of Genetics, Dept. of Physiol. and Genetics, Nat. Inst. of Agric. Sciences, Kannondai, Yatabe, Tsukuba, Japan, Pages 30-31. PA0 Palmer, J. D., Shields, C. R., Cohen, D. B., and Orton, T. J. (1983). "An Unusual Mitochondrial DNA Plasmid in the Genus Brassica". Nature 301:725-728. PA0 Rousselle, P., and Renard, M. (1982) "Interet du cultivar &lt;&lt;Bronowski&gt;&gt; pour l'obtention de plantes male-steriles cytoplasmiques chez le colza (Brassica napus L.)" Agronomie 2 (10):951-956. PA0 Shiga, T. (1976). "Studies on Heterosis Breeding Using Cytoplasmic Male Sterility in Rapeseed. Brassica napus L.", Bull. Nat. Inst. Agric. Sci. Tokyo Series D. 27:75-85. PA0 Shiga, T. (1976). "Cytoplasmic Male Sterility and Its Utilization for Heterosis Breeding in Rapeseed, Brassica napus L.", JARQ 10:177-182. PA0 Shiga, T. (1980). "Male Sterility and Cytoplasmic Differentiation". Chapter 12 in Brassica Crops and Wild Allies-Biology and Breeding. Japan Sci. Soc. Press, Tokyo, Pages 205-221. PA0 Thompson, K. F. (1972). "Cytoplasmic Male-Sterility in Oil-Seed Rape". Heredity 29(2):253-257. PA0 Vedel, F., Mathieu, C., Lebacq, P., Ambard-Bretteville, F., and Remy, R. (1982). "Comparative Macromolecular Analysis of the Cytoplasms of Normal and Cytoplasmic Male Sterile Brassica napus". Theor. Appl. Genet. 62:255-262. PA0 (a) growing in a first planting area a substantially random population of (1) cytoplasmic male sterile plants which exhibit cytoplasmic herbicide tolerance, and (2) male fertile plants which are capable of pollinating the cytoplasmic male sterile plants and which lack cytoplasmic herbicide tolerance, whereby the cytoplasmic male sterile plants (1) and the male fertile plants (2) are pollinated with pollen derived from the male fertile plants and seed is formed on the cytoplasmic male sterile plants and on the male fertile plants, PA0 (b) harvesting in bulk the seed which is formed on the plants of the first planting area, PA0 (c) growing at least a portion of the seed from step (b) in a second planting area in the absence of segregation between the seed derived from the cytoplasmic male sterile plants which exhibit cytoplasmic herbicide tolerance and the male fertile plants which lack cytoplasmic herbicide tolerance, and PA0 (d) contacting substantially all of the plants present in the second growing area prior to pollination with a herbicide which is effective to destroy the plants resulting from seed formed on the male fertile plants of the first planting area, whereby a substantially homogeneous population of a predetermined hybrid variety is formed which resulted from seed formed on the male sterile plants of the first planting area. PA0 (a) growing in a planting area a substantially random population of (1) cytoplasmic male sterile plants which exhibit cytoplasmic herbicide tolerance, and (2) male fertile plants which are capable of pollinating the cytoplasmic male sterile plants and which lack cytoplasmic herbicide tolerance, whereby the cytoplasmic male sterile plants (1) are pollinated with pollen derived from the male fertile plants (2), PA0 (b) contacting substantially all of the plants present in the growing area following the pollination with a herbicide which is effective to destroy the male fertile plants and which is ineffective to destroy the cytoplasmic male sterile plants, and PA0 (c) harvesting seed from the cytoplasmic male sterile plants which is capable of forming the hybrid plants in the substantial absence of seed from the male fertile plants which initially grew in the planting area. PA0 (1) a first rape plant component which exhibits cytoplasmic male sterility and cytoplasmic atrazine tolerance when applied as a foliar spray at a rate of 2 kilograms per hectare, and PA0 (2) a second rape plant component which is capable of pollinating the first rape plant component, is a homozygous recessive maintainer for the cytoplasmic male sterility of the first rape plant component, and which lacks atrazine tolerance when applied as a foliar spray at a rate of 2 kilograms per hectare. PA0 (1) a first rape plant component which exhibits cytoplasmic male sterility and cytoplasmic atrazine tolerance when applied as a foliar spray at a rate of 2 kilograms per hectare, and PA0 (2) a second rape plant component which is capable of pollinating the first rape plant component, is a homozygous dominant fertility restorer for said first rape plant component, and which lacks atrazine tolerance when applied as a foliar spray at a rate of 2 kilograms per hectare.
It has also been recognized in the past that weed control is an important consideration for those who choose to grow rape. Unchecked weeds will lessen the ultimate yield and can significantly reduce the quality by unavoidable contamination from diverse seeds which are harvested along with the desired crop. In order to deal with the weed problem various herbicide tolerant varieties of rape have been proposed so that unwanted weeds can be efficiently eliminated while growing in close proximity to the rape plants. See in this regard, "Transfer of Cytoplasmically-Inherited Triazine Resistance From Bird's Rape to Cultivated Oilseed Rape (Brassica campestris and B. napus)", by W. D. Beversdorf, J. Weiss-Lerman, L. R. Erickson and V. Souza Machado appearing in the Canadian Journal of Genetics and Cytology, Volume XXII, No. 2, June 1980, Pages 167-172. See also "Uniparental Inheritance of Chloroplast Atrazine Tolerance in Brassica Campestris" by V. Souza Machado, J. D. Bandeen, G. R. Stephenson and P. Lavigne, Can. J. Plant Sci. 58:977-981, 1978.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination wherein the seed-parent is cytoplasmic male sterile and wherein the pollen parent conveniently may be grown in bulk with the seed parent during at least one step of the process without the need for a precise planting pattern and the disadvantages associated therewith.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop wherein the cross-fertilization of cytoplasmic male sterile plants with maintainer plants readily may be accomplished.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination wherein the desired product may be formed on a reliable basis.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined variety of a crop which is capable of undergoing both self-pollination and cross-pollination which is suitable for utilization on an economical basis on a commercially attractive scale.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined variety of a crop which is capable of undergoing both self-pollination and cross-pollination wherein the desired product additionally exhibits herbicide tolerance which makes possible the selective destruction with ease of troublesome weeds growing within the hybrid crop area.
It is an object of the present invention to provide an improved hybridization process which particularly is suited for use when forming a predetermined variety of rape (e.g., Brassica napus), and to thereby provide a commercially practicable route for forming hybrid rape.
It is a further object of the present invention to provide a new and useful Brassica napus seed product which is suitable for use when carrying out the process of the present invention.
These and other objects and advantages will be apparent to those skilled in the art from a reading of the following description and appended claims.